An electrostatic paint system consists of a paint booth or enclosure in which a coating such as paint powder is applied to parts, a conveyor for carrying parts into and out of the booth, and an electrostatic paint applying system. The paint applying system includes a powder spraying device which imparts a velocity to the paint powder particles which directs them toward the device to be painted, places and electrical charge on the powder particles, creates an electrical field between the device being painted and ground, and meters the powder. Electrostatically-charged powder particles are attracted to and have an affinity for the grounded object to be painted since the grounded object assumes a polarity opposite that of the powder-spraying device. The charged powder particle, acted upon by the electrical field, can be deflected from its original trajectory in the direction of the grounded object.
In an automatic electrostatic system, the spraying device may be mounted in a fixed position, attached to a gun mover device that provides reciprocating motion, attached to a robot that imparts a predetermined complex motion, or manipulated manually. An electrostatic adhesion system greatly increases powder transfer efficiency from the gun to the surface to be coated as compared to a non-electrostatic device.
The paint powder that does not adhere to the part is generally referred to as overspray. Overspray consists of powder that misses the part, rebounds from the part surface, and powder electrostatically deflected to other grounded surfaces such as spray booth metal components and article conveyors. Most overspray is entrained in the spray booth exhaust air. This invention relates to an improved means for recovery of overspray entrained in spray booth exhaust air, particularly wherein varying colors are employed in successive runs.
Electrostatic powder spray users generally use either a cyclone type powder recovery system or a cartridge filter type powder recovery system.
Cartridge systems are very efficient, recovering nearly all powder overspray for reuse. However, the shortcoming of cartridge systems is that separate cartridge cabinets are required for each color to be run wherein separate cartridge cabinets, each dedicated to the recovery of only one particular color, are employed. That is, it is very difficult and time-consuming to completely clean the cartridge cabinets. Thus, dedicated cartridge cabinets are interchanged wherein a cabinet dedicated to a given color is installed when running that color, and replaced with another cabinet dedicated to the particular color to be run next. A primary concern in changing between successive colors is the prevention of intermixing of colors between successive runs. Even a small quantity of one color contaminating a second different color will result in an undesirable speckling effect. This intermixing prevention is the reason for utilization of independent cartridge booths for each separate color. The cost of maintaining such multiple cartridge booths for each separate color denies many users the ability to utilize a large number of colors, and also prohibits such users from limited runs of infrequently-used or custom colors.
In comparison, conventional cyclones alone normally recover only approximately 80% to 90% of oversprayed powder. A scrap collector is employed to trap the remainder of the powder. Powder from the scrap collector is speckled and must therefore, be disposed of. Thus, cyclones are not as efficient as cartridges. In long runs, this difference in efficiency can result in a substantial difference in powder usage and, accordingly, cost of operation. However, cyclones are advantageous in that, unlike cartridges, cyclones can be completely cleaned between successive runs of differing colors in a relatively short time. Thus, since one cyclone can be easily cleaned after a color run, it is not necessary to employ separate cyclones for each color to be run. Accordingly, short runs of specialized colors can be performed much more economically than with cartridge systems, which require separate cartridges for each specialized color to be run.
Currently users have to choose between either cartridge systems or cyclone systems. It is desirable to provide a single powder recovery system which provides both the nearly complete powder recovery attainable from cartridge systems and the color flexibility attainable from cyclone systems. It is also desirable to provide such an apparatus wherein separate cartridge cabinets and cyclone modules can be interchanged as desired to suit the needs of any particular user.